One year ago, a team of researchers showed that a diet rich in plant compounds lowers the risk of breast cancer in women after menopause. These compounds are called phytoestrogens and they attach to the receptors for the female sexual hormone estrogen.

The lead researcher, Prof. Dr. Jenny Chang-Claude, lead the studies showing the therapeutic effects of these compounds. Now, Heidelberg researchers want to know if phytoestrogens have any influence on the course of breast cancer development.

Lignans are regarded as the most significant kind of phytoestrogens in the Western diet. Lignans are found in seeds, especially flaxseeds, including wheat and vegetables. This phytoestrogen is converted to enterolactone in the intestines, which is then absorbed by the mucous tissue and serves as a biomarker in the patients’ blood.

The research team of Dr. Chang-Claude in one study took blood samples of 1140 women diagnosed with postmenopausal breast cancer. After an average observatory time of 6 years, they found a correlation between enterolactone levels and clinical disease progression.

The researchers found that the women with the highest enterolactone levels had a 40 percent lower risk of death, when compared to patients with the lowest enterolactone levels. Additionally, when scientists factored in the prevalence of metastasis and secondary tumors, the found a similar conclusion: “Women with the highest enterolactone levels also had a lower risk for such an unfavorable disease progression.”

“We now have first clear evidence showing that lignans lower not only the risk of developing postmenopausal breast cancer, but also the mortality risk,” says Jenny Chang-Claude. Past studies have tried to establish lignin intake by way of a dietary survey, however, such surveys are often unreliable and different people process plant chemicals in different ways. The researchers then decided to use a more reliable measurement of biomarkers.

“The result was significant only for the group of tumors that have no receptor for the estrogen hormone (ER-negative tumors). This gives reason to suspect that enterolactone protects from cancer not only by its hormone-like effect. Indeed, studies of cells and animals had already provided evidence suggesting that the substance also has an influence on cancer growth irrespective of estrogen. Thus, it promotes cell death and inhibits sprouting of new blood vessels.”

“In order to find out whether enterolactone also inhibits the aggressiveness of estrogen receptors in estrogen-positive tumors, we would need to expand this study to include much larger groups of women," said Dr. Chang-Claude. "By eating a diet that is rich in wholemeal products, seeds and vegetables, which is considered to be health-promoting anyway, everybody can take in enough lignans. At the present time, we can only discourage people from taking any food supplements.”

Since this is only a correlational study, we cannot definitively prove that plant chemicals are protective against cancer. However, Dr. Chang-Claude still recommends eating many vegetables.

“It has not yet been finally determined whether lignans in the body imitate the hormone effect or, on the contrary, counteract it,” says Dr. Chang-Claude. “Our studies will help achieve more clarity in this important question, which also concerns our daily diet."